But officials in the four cities also believe such a large fleet order will also demonstrate the purchasing power of local governments.

Los Angeles officials, for example, hope the request will encourage manufacturers to offer a wider array of electric vehicles by helping to create a larger market among fleet buyers for them.

"The hope is that by next month there could be additional cities in the request that hopefully brings the demand for EVs to 50,000 or perhaps even 100,000," said Matt Petersen, chief sustainability officer for Los Angeles Mayor Eric Garcetti.